1. Technical Field
This invention relates to a locking pin operating system for securing a sliding undercarriage to the suspension frame of a semitrailer. More particularly, the present invention relates to the driver assemblies that drive the locking pins from an engaged position to a disengaged position and then back again to the engaged position. Specifically, the present invention relates to a locking pin operating system that includes a single manually-operated valve that selectively directs pressurized air to expandable chambers wherein expansion of the chambers drives locking pins to disengaged positions while release of the pressurized air from the chambers allows springs to drive the locking pins to the engaged positions.
2. Background Information
In the United States, a tractor/semitrailer combination has been one of the most common modes of transportation of goods since World War II. The tractor/semitrailer combination includes a tractor having an engine, transmission, steerable front axle with wheels, and one or more rear drive axles and wheels. The tractor is attached to the semitrailer through a fifth wheel which is located over the tractor's rear drive axle. The semitrailer is unpowered and rides on one or more axles having a plurality of wheels. The semitrailer also includes a braking system and a suspension that are operated and adjusted from the tractor.
As the use of tractor/semitrailers grew over the years and their size increased, federal and state laws were passed that limit the weight per axle for tractors and semitrailers. It thus became desirable to be able to shift the load of the trailer to more evenly distribute its weight over the various axles. In order to redistribute the weight, a sliding undercarriage was developed that allows the relative position of the semitrailer's load to be adjusted with respect to the axles of the semitrailer. A sliding undercarriage typically includes a pair of slider rails having a linear array of locking pin holes disposed along their length. The slider rails slidably engage the frame of the suspension for the semitrailer and are held thereto by various devices. One device that holds the relative position of the slider rails with respect to the suspension frame is a locking pin. A sliding undercarriage typically includes two or four locking pins disposed about the corners of the suspension frame.
When the locking pins are engaged between the slider rails and the frame, the slider rails and load carrying portion of the semitrailer cannot be adjusted with respect to the wheels and suspension frame. The locking pins must be retracted to a disengaged position to allow the load carrying portion of the semitrailer to be adjusted along the suspension frame.
Both non-manual and manual systems are known in the art for moving the locking pins from an engaged position to a disengaged position and back to the engaged position. One manual system includes a handle connected to a torsion bar. A plurality of links connect each locking pin to the torsion bar. When adjustment of the semitrailer is required, the driver locks the brakes on both the tractor and semitrailer. The driver then climbs out of the tractor, walks to the sliding undercarriage, and pulls or lifts the manually operated locking pin release handle. This handle is typically positioned adjacent the wheels carried by the suspension frame. The pulling or lifting of the handle transmits a force through the links which overcomes the spring-loaded locking pins causing them to move to a disengaged position. The manual system typically includes means for holding all of the pins in the disengaged position while the driver returns to the tractor to reposition the sliding undercarriage. To reposition the undercarriage, the driver releases the brakes on the tractor while leaving the brakes on the semitrailer's sliding undercarriage engaged. The tractor is then driven forward or backward to slide the semitrailer relative to the sliding undercarriage. The driver then reapplies the tractor brakes and leaves the tractor to return to the sliding undercarriage to release the handle allowing the pins to return to the engaged position. Unfortunately, the spring-loaded locking pins are not usually perfectly aligned with the locking pin holes such that they all may not slide directly back into the engaged position. When this occurs, the driver returns to the tractor, releases the tractor brakes, and moves the semitrailer or rocks the semitrailer until the spring-loaded pins align with the locking pin holes and return to the engaged position. The driver must then reapply the brakes and walk around the semitrailer to visually verify that all pins are in the engaged position. The manually operated pin retraction systems, such as the one described above, often become impossible to operate due to damage or corrosion of the linkages and contamination with dirt or ice from exposure to the elements. The locking pins themselves can also become stuck in the locking pin holes when the semitrailer is parked on an incline or positioned with a twist in the frame. A common occurrence is that the driver will use a hammer to pound the locking pins from the engaged position to the disengaged position. Such hammering often damages the pins causing future operation of the manual system to be difficult.
In view of these problems with the manual system, non-manual systems using compressed air delivered from the braking system of the semitrailer were developed. One example of such a system can be found in U.S. Pat. No. 5,314,201. Still other improvements to that system may be found in U.S. Pat. Nos. 5,465,990, 5,564,727, and 5,620,195. These systems utilize compressed air delivered from the tractor to operate the braking and suspension systems of the semitrailer to move the locking pins between engaged and disengaged positions. These systems employ piston/cylinder combinations connected to the locking pins whereby selective delivery of pressurized air to the piston/cylinder causes the locking pin to move. Although these non-manual systems provide significant improvements over the manual system discussed above, improved driver assemblies and operating system configurations are still desired in the art.
For instance, the air cylinders used in the prior art to drive the locking pins between the engaged and disengaged positions are relatively exposed to the elements and unprotected from debris that may be thrown up from the road by the rear wheels of the tractor. It is thus desired in the art to provide a driver assembly that protects its moving parts from the elements to prevent or at least hinder the negative effects of water, salt, snow, and ice on the driver assembly. Another undesirable aspect of the driver assemblies of the prior art is their relative size. It is desirable to provide a driver assembly that is as compact as possible so that it may be fit onto various types of trailers without modification of the trailer. One difficulty with providing a compact driver assembly is that the locking pins are relatively long compared to the portion of the locking pin that actually locks the semitrailer body to the sliding undercarriage frame. Furthermore, the air cylinders disclosed in the prior art are relatively long with their pistons extending therefrom to further increase their length. It is also desired in the art to provide a compact, weather resistant driver assembly for a locking pin system that provides an accommodating or flexible connection between the locking pin and the driver assembly to accommodate movement of the locking pin with respect to the frame.